Positive resist composition and method of forming resist pattern

ABSTRACT

There is provided a positive type resist composition comprising (A) a resin component with only units derived from an acrylate ester in the principal chain, for which the solubility in alkali increases under the action of acid, (B) an acid generator component which generates acid on exposure, and (C) an organic solvent component, wherein the resin component (A) is a copolymer comprising (a1) a structural unit derived from an acrylate ester comprising, as an acid dissociable dissolution inhibiting group on a side chain, a polycyclic dissolution inhibiting group which is eliminated more easily than a 2-methyl-2-adamantyl group, (a2) a structural unit derived from an acrylate ester comprising a lactone containing polycyclic group on a side chain, and (a3) a structural unit derived from an acrylate ester comprising a hydroxyl group containing polycyclic group on a side chain; as well as a resist pattern formation method using such a composition.

TECHNICAL FIELD

The present invention relates to a positive type resist composition anda resist pattern formation method, and more specifically relates to achemically amplified positive type resist composition suitable for usein a process using a wavelength of no more than 200 nm, and particularlyan ArF excimer laser, as the light source, as well as a resist patternformation method using such a composition.

BACKGROUND ART

Until recently, polyhydroxystyrenes or derivatives thereof in which thehydroxyl groups are protected with an acid dissociable, dissolutioninhibiting group, which display high transparency relative to a KrFexcimer laser (248 nm), have been used as the resin component ofchemically amplified resists.

However, these days, the miniaturization of semiconductor elements hasprogressed even further, and the development of processes using ArFexcimer lasers (193 nm) is being vigorously pursued.

For processes using an ArF excimer laser as the light source, resinscomprising a benzene ring such as polyhydroxystyrene have insufficienttransparency relative to the ArF excimer laser (193 nm).

In order to resolve this problem, resins containing no benzene rings,but instead comprising a unit derived from a (meth)acrylate esterincorporating an adamantane ring within the principal chain areattracting considerable interest, and many materials have already beenproposed (Japanese Patent (Granted) Publication No. 2881969, JapaneseUnexamined Patent Application, First Publication No. Hei 5-346668,Japanese Unexamined Patent Application, First Publication No. Hei7-234511, Japanese Unexamined Patent Application, First Publication No.Hei 9-73173, Japanese Unexamined Patent Application, First PublicationNo. Hei 9-90637, Japanese Unexamined Patent Application, FirstPublication No. Hei 10-161313, Japanese Unexamined Patent Application,First Publication No. Hei 10-319595 and Japanese Unexamined PatentApplication, First Publication No. Hei 11-12326). The term(meth)acrylate ester refers to acrylate esters or methacrylate esters.

In these publications, as can be seen in Japanese Unexamined PatentApplication, First Publication No. 2001-131232 and Japanese UnexaminedPatent Application, First Publication No. 2001-142212, but also true forthe preceding technology described above, the materials comprising aunit derived from a (meth)acrylate ester within the principal chain areproposed without any discrimination between the acrylate ester and themethacrylate ester, although in the examples, materials with methacrylicacid as the principal chain are used, and practical applications alsoutilize materials with methacrylic acid in the principal chain.

The reason for this observation is that a resin with a conventionalacrylate ester as the principal chain (hereafter, simply referred to asan acrylate ester resin), as disclosed in the above publications,displays a lower Tg value than a resin with a methacrylate ester as theprincipal chain (hereafter, simply referred to as a methacrylate esterresin). More specifically, this Tg value is considerably lower thanconventional prebake temperatures of 120 to 140° C. and PEB (postexposure baking) temperatures of 120 to 130° C. required in chemicallyamplified resist compositions for vaporizing the solvent and forming theresist film, and enabling the acid generated from the acid generator toeliminate the acid dissociable, dissolution inhibiting groups, and inthese processes, or even in processes with a lower temperaturerequirement of, for example, approximately 20° C. lower, formation of aresist pattern was impossible.

However, with the development of different etching films in recentyears, a variety of etching gases can now be used, and as a result, anew problem has arisen in that surface roughness appears on the resistfilm following etching.

This surface roughness is different from conventional dry etchingresistance, and in a film etched using a resist pattern as a mask,appears as distortions around the hole patterns in a contact holepattern or as line edge roughness in a line and space pattern. Line edgeroughness refers to non-uniform irregularities in the line side walls.

Furthermore, in addition to the surface roughness generated followingetching, line edge roughness also occurs in the resist pattern followingdeveloping. This line edge roughness following developing also appearsas distortions around the hole patterns in a contact hole pattern or asnon-uniform irregularities in the line side walls in a line and spacepattern.

In addition, the design rules required in modern semiconductor elementproduction continue to become more stringent, and a resolution of nomore than 150 nm, and in the vicinity of 100 nm is necessary, andfurther improvements in resolution are keenly sought. In resist patternsrequiring this type of high resolution, distortions around the holepatterns or line edge roughness such as that described above becomes alarger problem than in conventional patterns.

In addition, resolving line slimming is also desirable. Line slimming isa phenomenon in which during observation of a resist pattern using ascanning electron microscope (SEM), the formed resist pattern shrinksand narrows. The cause of line slimming is reported to be due to thefact that when the formed resist pattern is exposed with the electronbeam used in a SEM, a cross linking reaction occurs, causing slimming[Journal of Photopolymer Science Technology, Vol. 13, No. 4, page 497(2000)].

As the design rules become tighter, this type of line slimming problemhas an increasing effect on the production of semiconductor elements,and consequently improvements are keenly sought.

DISCLOSURE OF INVENTION

The present invention has an object of providing a chemically amplifiedpositive type resist composition which displays excellent sensitivityand resolution, and enables the formation of a finely detailed resistpattern with low levels of surface roughness on etching, line edgeroughness and line slimming.

The inventors of the present invention discovered that although amethacrylate ester resin is ideal for resist pattern formation in so faras the Tg value is high, the above type of surface roughness isprevalent in a resist formed using a methacrylate ester resin, and themethacrylate ester resin is the cause of the surface roughness.

In other words, the present invention provides a positive type resistcomposition comprising (A) a resin component with only units derivedfrom an acrylate ester in the principal chain, for which the solubilityin alkali increases under the action of acid, (B) an acid generatorcomponent which generates acid on exposure, and (C) an organic solventcomponent, wherein the resin component (A) is a copolymer comprising(a1) a structural unit derived from an acrylate ester comprising, as anacid dissociable dissolution inhibiting group, a polycyclic dissolutioninhibiting group which is eliminated more easily than a2-alkyl-2-adamantyl group, (a2) a structural unit derived from anacrylate ester comprising a lactone containing polycyclic group, and(a3) a structural unit derived from an acrylate ester comprising ahydroxyl group containing polycyclic group.

Furthermore, the present invention also provides a resist patternformation method comprising the steps of providing a positive typeresist composition described above on a substrate, conducting a prebakeat 100 to 120° C. for 40 to 120 seconds, performing selective exposure,and then conducting PEB (post exposure baking) at 90 to 110° C. for 40to 120 seconds, and performing alkali developing.

BEST MODE FOR CARRYING OUT THE INVENTION

In a positive type resist composition of the present invention, a resincomponent (A) must be a resin component which does not comprise, in theprincipal chain, any structural units derived from methacrylate esterswhich cause resist surface roughness, but comprises only structuralunits derived from acrylate esters, and for which the solubility inalkali increases under the action of acid. Furthermore, because acomposition of the present invention is a positive type resistcomposition, the resin component (A) must have acid dissociable,dissolution inhibiting groups, and these groups must undergo eliminationin the presence of acid generated by an acid generator, altering theresin from an alkali insoluble state to an alkali soluble state, or inother words, increasing the alkali solubility.

In addition, in a positive type resist composition of the presentinvention, this resin component (A) must be a copolymer comprising (a1)a structural unit derived from an acrylate ester comprising, as an aciddissociable dissolution inhibiting group, a polycyclic dissolutioninhibiting group which is eliminated more easily than a2-methyl-2-adamantyl group, (a2) a structural unit derived from anacrylate ester comprising a lactone containing polycyclic group, and(a3) a structural unit derived from an acrylate ester comprising ahydroxyl group containing polycyclic group.

In this manner, by introducing a polycyclic group into all of theessential structural units, the Tg value is increased, the problem oflow Tg values associated with acrylate ester resins can be improved, andresist pattern formation can be achieved at temperatures slightly lowerthan conventional processes, namely, 100 to 120° C. for prebake, and 90to 110° C. for PEB.

Examples of the polycyclic group incorporated within each structuralunit include bicycloalkanes, tricycloalkanes and tetracycloalkanesgroups, including groups in which one hydrogen atom is removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane and tetracyclododecane, and these can be selectedappropriately from the multitude of groups proposed for use with ArFresists. Of the above groups, adamantyl groups and norbornyl groups arepreferred, although the groups may be selected appropriately inaccordance with the purpose of each of the structural units.

As follows is a description of each of the structural units of the resincomponent (A).

The structural unit (a1) is a structural unit derived from an acrylateester comprising, as an acid dissociable dissolution inhibiting group, apolycyclic dissolution inhibiting group which is eliminated more easilythan a 2-methyl-2-adamantyl group. It is evident that the introductionof a polycyclic group is successful in increasing the Tg value of theresin component (A), and in order to ensure that the resist pattern canbe formed at as low a temperature as possible, the acid dissociabilitymust be increased. As a result, the acid dissociable, dissolutioninhibiting group of the structural unit (a1) must be eliminated moreeasily than a 2-methyl-2-adamantyl group, which is a representative aciddissociable group for an ArF positive type resist.

Provided the structural unit (a1) has these types of properties, thereare no particular restrictions on the structural unit, although specificexamples include at least one type of structural unit selected from thegeneral formulas (I) and (II) shown below.

(wherein, R¹ represents a lower alkyl group of at least 2 carbon atoms)

(wherein, R² and R³ each represent, independently, a lower alkyl group)

Here, the aforementioned lower alkyl groups are preferably alkyl groupsof no more than 5 carbon atoms.

In the structural unit represented by the general formula (I), byensuring that R¹ is an alkyl group of at least 2 carbon atoms, the aciddissociability improves compared with the case in which R¹ is a methylgroup. Suitable examples of R¹ include straight chain or branched chainalkyl groups such as ethyl groups, propyl groups, isopropyl groups,n-butyl groups, isobutyl groups, tert-butyl groups, pentyl groups,isopentyl groups and neopentyl groups, although from an industrialviewpoint, ethyl groups are preferred.

Furthermore, in the structural unit represented by the general formula(II), by ensuring that R² and R³ each represent, independently, a loweralkyl group of 1 to 5 carbon atoms, the acid dissociability can beincreased beyond that of a 2-methyl-2-adamantyl group. Examples ofsuitable groups for both R² and R³ include methyl groups, or the samealkyl groups as the lower alkyl groups described above in relation toR¹, and of these, structural units in which both R² and R³ are methylgroups are preferred industrially.

Next, the structural unit (a2) is a structural unit derived from anacrylate ester comprising a lactone containing polycyclic group. Lactonecontaining polycyclic groups are effective in increasing the adhesionbetween the resist layer and the substrate, and in improving theaffinity with the developing liquid. There are no particularrestrictions on the group, provided the lactone containing polycyclicgroup of the structural unit (a2) is a lactone containing polycyclicgroup, although specifically, lactone containing bicycloalkyl groups,and particularly the structural unit represented by the chemical formulashown below, provide a good balance between the Tg value raising effectfor the resin component (A), and the lithography characteristics of theresist, and are consequently preferred.

The structural unit (a3) is a structural unit derived from an acrylateester comprising a hydroxyl group containing polycyclic group. Thisstructural unit contains a polar group such as a hydroxyl group, andconsequently improves the overall affinity of the resin component (A)with the developing liquid, and improves the alkali solubility of theexposed sections. Accordingly, this structural unit contributes toimproved resolution.

There are no particular restrictions on the group, provided the hydroxylgroup containing polycyclic group of the structural unit (a3) is ahydroxyl group containing polycyclic group, although specifically,hydroxyl group containing adamantyl groups, and particularly thestructural unit represented by the chemical formula shown below, providea good balance between the Tg value raising effect for the resincomponent (A), and the lithography characteristics of the resist, andare consequently preferred.

In the resin component (A) of a positive type resist composition of thepresent invention, if the combined total of the structural unit (a1),the structural unit (a2), and the structural unit (a3) is deemed 100 mol%, then resins in which the structural unit (a1) accounts for 30 to 60mol %, and preferably 35 to 45 mol %, the structural unit (a2) accountsfor 20 to 60 mol %, and preferably 25 to 35 mol %, and the structuralunit (a3) accounts for 10 to 50 mol %, and preferably 20 to 30 mol %,are preferred in terms of improving the balance between the reduction insurface roughness during etching, line edge roughness and line slimming,and the resolution.

The resin component (A) may also contain other structural units,provided such inclusion does not impair the effects of the presentinvention, although resins formed from the structural unit (a1), thestructural unit (a2) and the structural unit (a3) are preferred.

Furthermore, there are no particular restrictions on the weight averagemolecular weight of the resin component (A), although values from 5,000to 30,000 are preferred, and values from 8,000 to 20,000 are even moredesirable. If the weight average molecular weight is larger than thisrange, then the solubility relative to the resist solvent deteriorates,whereas if smaller than the above range, the shape of the resist patterncan deteriorate, which is also undesirable.

The resin component (A) can be produced easily by known radicalpolymerization of the corresponding acrylate ester monomer using aradical polymerization initiator such as azobisisobutyronitrile (AIBN).

On the other hand, an acid generator component (B) of a positive typeresist composition of the present invention, which generates acid onexposure, can be appropriately selected from known materials used asacid generators in conventional chemically amplified resists. Examplesof the acid generator include onium salts such as diphenyliodoniumtrifluoromethanephosphate, (4-methoxyphenyl)phenyliodoniumtrifluoromethanesulfonate, bis(p-tert-butylphenyl)iodoniumtrifluoromethanesulfonate, triphenylsulfonium trifluoromethanesulfonate,(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,(p-tert-butylphenyl)diphenylsulfonium trifluoromethanesulfonate,diphenyliodonium nonafluorobutanesulfonate,bis(p-tert-butylphenyl)iodonium nonafluorobutanesulfonate andtriphenylsulfonium nonafluorobutanesulfonate. Of these, onium salts witha fluorinated alkylsulfonate ion as the anion are preferred.

This radical acid generator component (B) may utilize a single compound,or a combination of two or more compounds. The quantity of the acidgenerator component (B) is typically selected within a range from 0.5 to30 parts by mass, and preferably 1 to 10 parts by mass per 100 parts bymass of the resin component (A). If the quantity is less than 0.5 partsby mass then the pattern formation does not proceed adequately, whereasif the quantity exceeds 30 parts by mass, then achieving a uniformsolution becomes difficult, causing a deterioration in storagestability.

A positive type resist composition of the present invention is used as asolution obtained by dissolving the aforementioned resin component (A)and the acid generator component (B) in an organic solvent (C). Providedthe solvent is capable of dissolving both components to generate auniform solution, then the solvent used can be one, or two or moresolvents selected from amongst known solvents used for conventionalchemically amplified resists.

Examples of this type of organic solvent (C) include ketones such asacetone, methyl ethyl ketone, cyclohexanone, methyl isoamyl ketone and2-heptanone; polyhydric alcohols and derivatives thereof such asethylene glycol, ethylene glycol monoacetate, diethylene glycol,diethylene glycol monoacetate, propylene glycol, propylene glycolmonoacetate, dipropylene glycol, or the monomethyl ether, monoethylether, monopropyl ether, monobutyl ether or monophenyl ether ofdipropylene glycol monoacetate; cyclic ethers such as dioxane; andesters such as methyl lactate, ethyl lactate, methyl acetate, ethylacetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methylmethoxypropionate, and ethyl ethoxypropionate. These organic solventsmay be used singularly, or as mixed solvents of two or more differentsolvents. In terms of mixed solvents, mixed solvents of propylene glycolmonomethyl ether acetate and a lactate ester are preferred. The mixtureratio is preferably a mass referenced ratio from 8:2 to 2:8.

In a positive type resist composition of the present invention, using amixed solvent containing at least one of propylene glycol monomethylether acetate and ethyl lactate, together with γ-butyrolactone as theorganic solvent is advantageous. In such a case, the mass ratio of theformer and latter components in the mixed solvent is selected within arange from 70:30 to 95:5.

In a positive type resist composition of the present invention, in orderto improve the resist pattern shape and the long term stability (thepost exposure stability of the latent image formed by the pattern-wiseexposure of the resist layer), a secondary lower aliphatic amine or atertiary lower aliphatic amine can also be added as a component (D).Here, a lower aliphatic amine refers to an alkyl amine or an alkylalcohol amine of no more than 5 carbon atoms, and examples of thesesecondary and tertiary amines include trimethylamine, diethylamine,triethylamine, di-n-propylamine, tri-n-propylamine, tripentylamine,diethanolamine and triethanolamine, and trialkanolamines areparticularly preferred.

These may be used singularly, or in combinations of two or morecompounds.

These amines are typically added in quantities within a range from 0.01to 0.2 mass % relative to the quantity of the resin component (A).

Miscible additives can also be added to a positive type resistcomposition of the present invention according to need, includingadditive resins for improving the properties of the resist film,surfactants for improving the ease of application, dissolutioninhibitors, plasticizers, stabilizers, colorants and halation preventionagents.

In a pattern formation method of the present invention, because theresin component (A) in the positive type resist composition of thepresent invention utilizes an easily eliminated, acid dissociable,dissolution inhibiting group in the structural unit (a1), patternformation can be conducted at a lower temperature than that used inconventional resist pattern formation processes. In other words, theresist composition is first applied to the surface of a substrate suchas a silicon wafer using a spinner, a prebake is conducted at 100 to120° C. for 40 to 120 seconds, and preferably for 60 to 90 seconds, andthen following selective exposure of an ArF excimer laser through adesired mask pattern using, for example, an ArF exposure apparatus, PEB(post exposure baking) is conducted at 90 to 110° C. for 40 to 120seconds, and preferably for 60 to 90 seconds. Subsequently, developingis conducted using an alkali developing liquid such as a 0.1 to 10 mass% aqueous solution of tetramethylammonium hydroxide. In this manner, aresist pattern which is faithful to the mask pattern can be obtained.

Furthermore, although a composition of the present invention isparticularly applicable to ArF excimer lasers, it is also effective forother types of radiation of shorter wavelength such as F₂ lasers, EUV(extreme ultraviolet radiation), VUV (vacuum ultraviolet radiation),electron beams, X-rays and soft X-rays.

EXAMPLES

As follows is a more detailed description of the present invention usinga series of examples.

In each of the examples, the surface roughness following etching and theline slimming were measured using the methods described below.

(1) Surface Roughness Following Etching:

Using a mixed gas of tetrafluoromethane (CF₄), trifluoromethane (CHF₃)and helium (flow rate ratio 30:30:100) as the etching gas, a resist filmformed by applying a resist composition to a substrate at a pressure of0.3 Torr and a temperature of 20° C., prebaking, exposing thecomposition without using a mask pattern and then performing PEB(hereafter, this resist film is described as an unpatterned resist film)was treated for 2 minutes using an etching apparatus (TCE-7612X, a tradename, manufactured by Tokyo Ohka Kogyo Co., Ltd.) using a RF (radiofrequency) of 400 kHz with an output of 600 W, and the surface followingthis dry etching was numericalized with an AFM (atomic forcemicroscope), and the Rms value (root mean square surface roughness),which is a value representing the surface roughness, was then evaluated.

The reason for performing the evaluation using an unpatterned resistfilm is that surface roughness can be more easily measured than in thecase of a patterned resist film.

(2) Line Slimming:

An isolated pattern was formed, and then using a measuring SEM (S-8820,a trade name, manufactured by Hitachi, Ltd.), the width of the resistpattern prior to, and following irradiation were measured and compared.(time affected by electron beam: approximately 30 seconds)

Example 1

Resin Component (A): 100 parts by mass of a copolymer formed fromstructural units represented by the structural formulas shown below(proportion x of structural unit (a1)=40 mol %, proportion y ofstructural unit (a2)=30 mol %, proportion z of structural unit (a3)=30mol %, weight average molecular weight: 14,000),

Acid Generator Component (B): 3 parts by mass of triphenylsulfoniumnonafluorobutanesulfonate, and component (D): 0.1 parts by mass oftriethanolamine were dissolved in an organic solvent component (C)comprising a mixed solvent of 450 parts by mass of propylene glycolmonomethyl ether acetate and 300 parts by mass of ethyl lactate,yielding a uniform positive type resist composition solution.

This solution was applied to the surface of a silicon wafer using aspinner and then prebaked for 90 seconds at 110° C. on a hotplate, andformed a resist layer with a film thickness of 400 nm. This film wasselectively irradiated with an ArF excimer laser (193 nm), using an ArFexposure apparatus (Micro Step, a trade name, manufactured by ISICorporation, NA=0.60, σ=0.75), subjected to PEB treatment at 100° C. for90 seconds, and was then subjected to puddle development for 60 secondsin a 2.38 mass % aqueous solution of tetramethylammonium hydroxide,washed for 30 seconds with water, and dried.

The hole resist pattern formed by the above operation provided smoothcircular shapes with a hole diameter of 130 nm and no distortion aroundthe periphery of the holes, and displayed no line edge roughness.

Furthermore, when the exposure time (sensitivity) was measured in unitsof mJ/cm² (quantity of energy), the result was 21 mJ/cm².

The depth of focus range of this 130 nm hole resist pattern was 300 nm.

The surface roughness of this resist film following etching was Rms 1.1nm, and in terms of line slimming, there was almost no variation, withthe original width of the resist pattern of 100 nm becoming 96 nmfollowing electron beam irradiation.

Example 2

With the exception of using a copolymer in which the proportions of x, yand z were 30 mol %, 50 mol % and 20 mol % respectively, a positive typeresist composition solution was prepared in the same manner as theexample 1.

Using this solution, a line and space pattern was formed under the samelithography conditions as the example 1.

As a result, a 130 nm line and space pattern was formed with a goodrectangular cross section and with good resolution. The sensitivity was11 mJ/cm². Furthermore, the line edge roughness of this pattern wasdetermined by measuring the resist pattern width of the sample at 32positions using a measuring SEM (S-9220, a trade name, manufactured byHitachi, Ltd.), and from these measurement results, the value of 3 timesthe standard deviation (3σ) was calculated. The smaller this 3σ valueis, the lower the level of roughness, indicating a resist pattern with auniform width. The value of 3σ was 4.2 nm.

The Rms value, which is a measure of the surface roughness of the resistpattern, was 1.6 nm, and in terms of line slimming there was almost novariation, with the value of 100 nm prior to electron beam irradiationbecoming 96 nm following irradiation.

Comparative Example 1

With the exception of using a resin component (A) in which the acrylateof the structural unit (a1) of the resin component (A) from the example1 was replaced with a methacrylate comprising a dissolution inhibitinggroup of the same structure, preparation was performed in the samemanner as the example 1, or in other words, with the exception ofsetting the proportion x of a structural unit of the structural formulashown below to 40 mol %, a positive type resist composition solution wasprepared in the same manner as the example 1.

Subsequently, using this solution, but with the exception of alteringthe lithography conditions to a prebake at 130° C. for 90 seconds andPEB at 120° C. for 90 seconds, a resist pattern was formed in a similarmanner to the example 1.

The hole resist pattern formed in this manner provided circular shapeswith a hole diameter of 130 nm and distortions around the periphery ofthe holes, displaying line edge roughness. Furthermore, the sensitivitywas 16 mJ/cm². The depth of focus range of this 130 nm hole resistpattern was 300 nm.

A 130 nm line and space pattern was also formed in a separatepreparation, and when the 3σ value was determined in the same manner asthe example 2 as a measure of the line edge roughness, the value was 8.8nm.

Furthermore in terms of line slimming, the value of 100 nm prior toelectron beam irradiation fell to 92 nm following irradiation.

Comparative Example 2

With the exception of using a resin component (A) in which thestructural unit (a1) of the resin component (A) from the example 1 wasreplaced with a 2-methyl-2-adamantyl acrylate, preparation was performedin the same manner as the example 1, or in other words, with theexception of setting the proportion x of a structural unit of thestructural formula shown below to 40 mol %, a positive type resistcomposition solution was prepared in the same manner as the example 1.

Subsequently, using this solution, a hole resist pattern was formedunder the same lithography conditions as the example 1, and a 130 nmline and space pattern was formed in the same manner as the example 2.

Although the hole resist pattern formed in this manner had a holediameter of 130 nm, the sensitivity exceeded 100 mJ/cm², andfurthermore, the cross-sectional shape of the 130 nm line and spacepattern was a taper shape, and the sensitivity was an unsatisfactory 60mJ/cm².

Furthermore using a separate solution, and with the exception ofaltering the lithography conditions to a prebake at 130° C. for 90seconds and PEB at 120° C. for 90 seconds, a hole resist pattern wasformed in a similar manner to the example 1, and a 130 nm line and spacepattern was formed in a similar manner to the example 2.

Although the thus formed hole resist pattern had a hole diameter of 130nm, the side walls thereof displayed a marked taper, and the depth offocus range of this 130 nm hole resist pattern was 0 nm.

Furthermore, the 130 nm line and space pattern had a triangularcross-section and was unsatisfactory.

In addition, the Rms value, which is a measure of the surface roughnessof the resist pattern, was 1.3 nm.

Comparative Example 3

With the exception of using a copolymer in which the proportion x of thesame structural unit (a1) as the example 1 was 50 mol % and theproportion y of the same structural unit (a2) as the example 1 was 50mol %, and in which there was no structural unit (a3), instead of theresin component (A) of the example 1, a positive type resist solutionwas prepared in the same manner as the example 1, and subsequently,using this solution, a hole resist pattern was formed in a similarmanner to the example 1, and a 130 nm line and space pattern was formedin a similar manner to the example 2.

Although the thus formed hole resist pattern formed in this manner had ahole diameter of 130 nm, the depth of focus range of the 130 nm holeresist pattern was 100 nm.

Furthermore, the 130 nm line and space pattern developed an inclination,and was unsatisfactory.

In addition, the Rms value, which is a measure of the surface roughnessof the resist pattern, was 0.9 nm.

As is evident from the above results, a hole resist pattern of a resistfilm using a positive type resist composition of the present inventionprovides a smooth circular shape with no distortions around theperiphery of the holes and no line edge roughness, and a line and spacepattern also displays a good rectangular cross section with goodresolution, with little roughness and a small Rms value which indicatessurface roughness. In addition, the sensitivity during formation ofthese patterns is also good. Line slimming is also almost non-existent.

In contrast, with a resist composition which instead of the acrylate ofthe structural unit (a1) used a methacrylate comprising a dissolutioninhibiting group of the same structure, a hole resist pattern displayeddistortions around the periphery of the holes, and also displayed lineedge roughness. Furthermore, it was also evident that the roughness of aline and space pattern was large, and line slimming occurred.

Furthermore, in the case in which 2-methyl-2-adamantyl acrylate was usedas the structural unit (a1), the sensitivity was inadequate, thecross-sectional shape of a line and space pattern was either tapered ora triangular shape, and the Rms value was larger than for a material ofthe present invention.

In the case in which a copolymer with no structural unit (a3) was used,the line and space pattern developed an inclination, and wasunsatisfactory.

INDUSTRIAL APPLICABILITY

A composition of the present invention is a chemically amplified typecomposition, and displays good transparency, a high level of sensitivityand a high resolution relative to activated light of less than 200 nm,and particularly ArF excimer laser light, and also produces a resistfilm following etching with little surface roughness, and little lineedge roughness in a line and space pattern. Furthermore, a detailedresist pattern with little line slimming when viewed with a scanningelectron microscope can also be provided. Accordingly, as a chemicallyamplified positive type resist using an ArF excimer laser as the lightsource, a composition of the present invention can be ideally used inthe production of semiconductor elements and the like which requireultra fine processing. Consequently, a composition of the presentinvention is extremely useful for industrial applications.

1. A positive type resist composition comprising: (A) a resin componentwith only units derived from an acrylate ester in a principal chain, forwhich solubility in alkali increases under action of acid; (B) an acidgenerator component which generates acid on exposure; and (C) an organicsolvent component, wherein said resin component (A) is a copolymerincluding (a1) a structural unit derived from an acrylate estercomprising, as an acid dissociable dissolution inhibiting group, apolycyclic dissolution inhibiting group which is eliminated more easilythan a 2-methyl-2-adamantyl group; (a2) a structural unit derived froman acrylate ester comprising a lactone containing norbornyl group; and(a3) a structural unit derived from an acrylate ester comprising ahydroxyl group containing polycyclic group, wherein said structural unit(a1) is represented by a chemical formula (I) shown below:

wherein, R¹ represents an ethyl group, said structural unit (a2) is aunit derived from an acrylate ester comprising a lactone containingbicycloalkyl group, and said structural unit (a3) is represented by achemical formula shown below

and, wherein if a combined total of said structural unit (a1), saidstructural unit (a2) and said structural unit (a3) is deemed 100 mol %,then said structural unit (a1) is within a range from 30 to 60 mol %,said structural unit (a2) is within a range from 20 to 60 mol %, andsaid structural unit (a3) is within a range from 10 to 50 mol %.
 2. Apositive type resist composition according to claim 1, wherein saidstructural unit (a2) is represented by a chemical formula shown below


3. A positive type resist composition according to claim 1, wherein saidacid generator component (B) is an onium salt with a fluorinatedalkylsulfonate ion as an anion.
 4. A positive type resist compositionaccording to claim 1, wherein in addition to said resin component (A),said acid generator component (B) and said organic solvent (C), asecondary or tertiary lower aliphatic amine (D) is also provided in aquantity of 0.01 to 0.2 mass % relative to a quantity of said resincomponent (A).
 5. A resist pattern formation method comprising the stepsof providing a positive type resist composition according to any one ofclaim 2, 3, or 4 on a substrate, conducting a prebake at 100 to 120° C.,performing selective exposure, and then conducting PEB (post exposurebaking) at 90 to 110° C., and performing alkali developing.
 6. Apositive type resist composition comprising: (A) a resin component withonly units derived from an acrylate ester in a principal chain, forwhich solubility in alkali increases under action of acid; (B) an acidgenerator component which generates acid on exposure; and (C) an organicsolvent component, wherein said resin component (A) is a copolymerincluding (a1) a structural unit derived from an acrylate estercomprising, as an acid dissociable dissolution inhibiting group, apolycyclic dissolution inhibiting group which is eliminated more easilythan a 2-methyl-2-adamantyl group, (a2) a structural unit derived froman acrylate ester comprising a lactone containing polycyclic group, and(a3) a structural unit derived from an acrylate ester comprising ahydroxyl group containing polycyclic group, wherein said structural unit(a1) is at least one unit selected from a group consisting of membersrepresented by a general formula (II) shown below:

wherein, R² and R³ are both methyl groups, said structural unit (a2) isa unit derived from an acrylate ester comprising a lactone containingnorbornyl group, and said structural unit (a3) is represented by achemical formula shown below

and, wherein if a combined total of said structural unit (a1), saidstructural unit (a2) and said structural unit (a3) is deemed 100 mol %,then said structural unit (a1) is within a range from 30 to 60 mol %,said structural unit (a2) is within a range from 20 to 60 mol %, andsaid structural unit (a3) is within a range from 10 to 50 mol %.
 7. Apositive type resist composition according to claim 6, wherein saidstructural unit (a2) is represented by a chemical formula shown below


8. A positive type resist composition according to claim 6, wherein saidacid generator component (B) is an onium salt with a fluorinatedalkylsulfonate ion as an anion.
 9. A positive type resist compositionaccording to claim 6, wherein in addition to said resin component (A),said acid generator component (B) and said organic solvent (C), asecondary or tertiary lower aliphatic amine (D) is also provided in aquantity of 0.01 to 0.2 mass % relative to a quantity of said resincomponent (A).
 10. A resist pattern formation method comprising thesteps of providing a positive type resist composition according to anyone of claim 6, 7, 8 or 9 on a substrate, conducting a prebake at 100 to120° C., performing selective exposure, and then conducting PEB (postexposure baking) at 90 to 110° C., and performing alkali developing.